The invention relates to braking systems and, more particularly, a method and apparatus for positioning an end of a push rod of a brake actuator.
Braking systems, such as air brake systems, have generally been used to control movement of motor vehicles in a safe and effective manner. In particular, air brakes are commonly used on commercial vehicles such as trucks, trailers, and buses, which typically have large gross vehicle weights. The considerable inertial mass of these heavy-duty vehicles in combination with the high speeds at which they travel often requires a braking system which responds rapidly with substantial braking power. One system component which may be instrumental in the operation of air brake systems is the brake actuator. The brake actuator typically provides the necessary force when braking the vehicle.
FIG. 1 depicts a push rod generally known in the art. The push rod is a component of brake actuator 12 and is commonly found in many air disc brake systems. As shown, push rod 10 typically extends outwardly away from a mounting face 17 of brake actuator 12. The end of push rod 10 engages with ball end 16 of arm 14, typically a socket part of arm 14. Usually, the overall length Lxe2x80x2 of push rod 10 and ball end 16 relative to mounting face 17 is important to proper braking. Because of such importance, the overall length Lxe2x80x2 may be adjustable. Traditional braking systems, as illustrated in FIG. 1, often used shims 18, or spacers, placed between ball end 16 and push rod 10 to variably adjust overall length Lxe2x80x2.
U.S. Pat. No. 5,579,873 to Kohar et al. (xe2x80x9cKoharxe2x80x9d) relates to a brake actuator system having calipers that may close upon a disc in order to apply the brakes. Similar to the push rod of FIG. 1, Kohar may also use spacers to operate as shims in adjusting the calipers.
It is typically accepted and known that the overall length of the push rod and ball end relative to a mounting face surface of the actuator is usually essential to proper functioning of the brake system. If this length is too short, a user may need to apply the brakes in a more vigorous manner to brake the vehicle than if the overall length was properly determined. If the overall length is too long, the brakes may be applied continuously or when a user does not wish the vehicle to be braked, which may cause premature wear on the brakes. Because of the importance of the overall length, using shims to variably adjust the overall length may negatively affect accurate determinations of this length, which may possibly affect braking performance.
Usually, the overall length is determined within an acceptable tolerance range. Similarly, the components that make up the overall length, namely the push rod, ball end, and any shims used, are also typically manufactured within a known tolerance range. Combining the components typically results in the combination of the tolerances of the individual components to determine the overall tolerance range. This combination of the tolerances is known in the art to be defined as a xe2x80x9ctolerance stack upxe2x80x9d. The more shims used, the larger the overall tolerance range may become. In some instances, especially where an accurate determination of the overall length is desired, the resulting tolerance stack up may be larger than the acceptable tolerance range for the overall length, resulting in the overall length to be out of tolerance. Furthermore, variability in the actual dimensions of the components that results in an out of tolerance overall length may necessitate provisions for adjustments in order to bring the overall length back within tolerance, such provisions in turn may contribute to tolerance stack up.
Another disadvantage of using shims is that it may increase set up time for positioning the push rod relative to the ball end. The more shims involved to position the push rod relative to the ball end, the more time is typically needed to choose the correctly sized shims or interchange shims. Furthermore, if components of the braking system are interchanged, such as parts of the brake actuator, the shims may shift out of position, thereby necessitating repositioning of the push rod relative to the ball end. This problem may be exacerbated if the combination of shims chosen are not suited to the components of the braking system, where variability between braking systems sometimes favor particular combinations of shims. Adhering the shims to one another may reduce set up time but may also exacerbate tolerance stack up due to the adhesive material now being placed between the shims and affecting the overall length.
What is desired, therefore, is a push rod and ball end assembly that provides an accurate determination of the overall length relative to the mounting face surface. Another desire is a push rod and ball end assembly that reduces tolerance stack up. A further desire is a push rod and ball end assembly that reduces variability in overall length caused by tolerance stack up. Still another desire is a push rod and ball end assembly that reduces set up time.
Accordingly, it is an object of the invention to provide a push rod and ball end assembly that has an accurately determined overall length and distance from a surface of an actuator""s mounting face.
It is another object of the invention to provide a push rod and ball end assembly that maintains its accurately determined overall length over prolonged use of the brake system.
It is another object of the invention to provide a push rod and ball end assembly that reduces set up time when interchanging components of a brake system.
These and other objects of the invention are achieved by provision of an apparatus for positioning components of a brake system, including a push rod, a ball end coupled to the push rod, and a force transfer member placed between the push rod and the ball end. The force transfer member has both a flowable property and a solidifying property, whereby the force transfer member is flowable when being placed between the push rod and ball end and, after a passage of time, the force transfer member solidifies.
In the preferred embodiment, the force transfer member is self hardening, where it automatically solidifies without user intervention. In other embodiments, an additive is added to the force transfer to solidify or facilitate solidifying the force transfer member.
The ball end may optionally include a hole extending from a first end and a second end of the ball end for permitting the force transfer member to be placed, or injected, between the push rod and ball end.
In another aspect of the invention, a method for positioning components of a brake system is provided, including the steps of providing a push rod of a brake actuator and providing a ball end. The method also includes the steps of positioning the push rod relative to the ball end, placing a force transfer member between the push rod and the ball end, and solidifying the force transfer member.
The method may optionally include the step of temporarily or permanently fixing the position of the push rod relative to the ball end.
Prior to placing the force transfer member between the push rod and ball end, or in embodiments where the ball end is temporarily fixed relative to the push rod, the method may optionally include the step of adjusting a distance of the ball end relative to a mounting face of the brake actuator.
Additionally, the method may optionally include the step of providing a hole in the ball end, wherein the hole extends an entire length of the ball end. This hole permits injection of the force transfer member through into the hole and in between the ball end and push rod.
To assist ensuring a proper amount of the force transfer member is placed between the ball end and push rod, the method may include adjusting a flow characteristic of the force transfer member, such as pressure, temperature, flow rate, and combinations thereof, as it is placed between the push rod and the ball end. The method may also continue to place the force transfer member between the push rod and ball end until a desired pressure is achieved.
For embodiments where the force transfer member is not self hardening, or does not automatically solidify without user intervention, the method may include the step of adding an additive to the force transfer member to facilitate solidification.